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Asymmetrical physiological cost of reproduction shapes caste-specific resource allocation in an ant, Diacamma cf. indicum from Japan

Tanaka, Yasunari1; Ishizuka, Yusuke2; Matsuura, Yu3; Jilin, Pan2; Shimoji, Hiroyuki3

Published Jan 16, 2026 on Dryad. https://doi.org/10.5061/dryad.ht76hdrvn

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Abstract

In eusocial insects, queens demonstrate high reproductive capacity and extended longevity, representing examples of the trade-off in resource allocation. Workers perform non-reproductive tasks, such as caring for broods and foraging, thus reducing the energetic demands of queens. As queens dedicate their lives to reproduction, these reduced energetic demands enable them to live longer, laying many eggs. However, the physiological specialisation of queens is markedly distinct from that of workers. This study examines the trade-off between immunocompetence and reproduction among castes in an ant species, Diacamma cf. indicum, from Japan, which lacks a morphological queen caste. First, gamergates (functional queens) exhibited higher expression of innate immunity genes than the workers. Second, to experimentally skew resource allocation toward immunocompetence, gamergates and reproductive workers were subjected to an immune challenge. As a result, the expression of the antimicrobial peptide gene Hymenoptaecin was increased in gamergates without compromising reproduction-related genes, such as Vitellogenin. In contrast, the expression of genes associated with reproduction was decreased in reproductive workers. Moreover, we revealed that gamergates possessed a remarkably low fat content, similar to non-reproductive foragers. These findings suggest that, while gamergates can overcome the trade-off, reproductive workers are constrained by the physiological costs of reproduction.